Solar panel systems: panel types, incentives, and the best tilt angle

What a photovoltaic system is: the photovoltaic effect

A photovoltaic system produces electricity through the photovoltaic effect: when sunlight strikes a semiconductor material, typically chemically treated silicon, it frees up electrons and generates a direct current. Individual cells are assembled into a panel (the module), several panels are wired together in series to form a string, and an inverter finally turns the direct current produced into the alternating current used by household appliances and fed into the grid.

It’s a physical process completely different from the photosynthesis plants rely on: there, light becomes chemical energy stored in a sugar molecule; here, it becomes a flow of electrons that registers immediately as electric current, with no chemical steps in between.

Cell types: from crystalline silicon to thin film

Photovoltaic cells fall into three generations, following a classification used in a 2020 technical report from ENEA, Italy’s national energy research agency, with market figures dated to 2017:

• First generation, crystalline silicon: monocrystalline, polycrystalline, and ribbon silicon. This family has the highest material purity (in the case of monocrystalline cells) and the best performance in terms of efficiency, at a higher production cost; polycrystalline cells, by contrast, can also be produced from recycled electronic-component scrap.
• Second generation, thin film: amorphous silicon (a-Si), cadmium telluride (CdTe), multi-junction cells, and copper indium gallium diselenide (CIGS/CIS). The active layer of an amorphous silicon cell can be up to 300 times thinner than a crystalline silicon cell, though at a lower efficiency.
• Third generation, emerging technologies: concentrator photovoltaics (CPV), dye-sensitized cells, organic and hybrid cells, and the PERC/PERL variants of crystalline silicon.

Back in 2017, crystalline silicon covered about 90% of the world market (40% monocrystalline, 48% polycrystalline, 2% ribbon silicon), with the remaining 9% split among thin-film technologies (5% cadmium telluride, 2% amorphous silicon, 2% CIGS). The picture has shifted dramatically in under a decade: according to the Photovoltaics Report from the Fraunhofer Institute for Solar Energy Systems (ISE), updated as of July 2026, world module production in 2025 totaled around 706 GWp, of which 690 GWp was monocrystalline silicon and zero was polycrystalline silicon, which has practically disappeared from large-scale industrial production; thin film accounted for between 2 and 3% of the market. Wafer-based silicon as a whole covered about 98% of total production.

Efficiency has climbed in step: average commercial efficiency of monocrystalline modules has risen from about 17% to just under 25% between roughly 2016 and 2026, while the laboratory record for a single monocrystalline silicon cell, as of May 2026, stands at 28.1%. The n-type TOPCon and Heterojunction (HJT) technologies are replacing the older p-type PERC technology as the market standard for commercial modules.

Technology	Generation	Lab efficiency record (2026)	Share of 2025 world production
Monocrystalline silicon	First	28.1%	nearly all wafer-based silicon (~98% of total)
Polycrystalline silicon	First	—	essentially zero
CIGS (thin film)	Second	23.4%	within the 2-3% thin-film share
CdTe (thin film)	Second	21.0%	within the 2-3% thin-film share
Perovskite and tandem	Third (emerging)	26.9% (perovskite) / 35.2% (silicon tandem)	not yet significant in the mass market

Laboratory record efficiency figures shouldn’t be confused with the efficiency of commercial panels, which is always lower: the two are different measurements, one obtained under controlled conditions on single cells, the other on modules produced at scale.

System types: from rooftop to floating panels

Beyond cell technology, a photovoltaic system can also be classified by how it’s installed. The most widely used terminology — integrated, partially integrated, non-integrated — comes from Italy’s old Conto Energia, the incentive program closed for good in 2013 and no longer active: that program’s tariffs no longer mean anything, but the three categories are still useful for describing how a system is physically installed. An integrated system uses modules or components designed to replace an architectural element (solar roof tiles, canopies, brise-soleil panels); a partially integrated system rests on the roof slope without replacing anything; a non-integrated system is typically a large ground-mounted installation.

A second distinction concerns the connection to the electrical grid. The large majority of systems in Italy are grid-connected (98% of Italian systems are connected at low voltage, according to the 2024 IEA-PVPS report): electricity produced and not consumed right away is fed into the grid and, as covered further below, can be sold. Stand-alone (off-grid) systems also exist: they aren’t connected to the grid and generate direct current used directly for specific needs, such as water pumping, lighting, or refrigeration, typically at sites without a grid connection.

More recent setups add to this picture, as noted in the Fraunhofer ISE 2026 Photovoltaics Report: agrivoltaic systems, which combine electricity generation with farming on the same land (with modules arranged between crop rows, above the rows, or vertically between them), floating solar systems on bodies of water, and the first products of photovoltaics integrated into vehicles.

Practical example: in 2024, in Italy, new photovoltaic systems of every kind (not just residential) had an average capacity of 23.8 kW; systems under 10 kW, nearly all of them residential, made up 85% of the total number of installations but only 21% of national capacity, because the rest of the capacity comes from a much smaller number of large commercial and ground-mounted systems — a typical residential system, then, sits well below that 23.8 kW overall average.

Solar incentives in Italy in 2026

The first tool available in Italy in 2026 is fiscal: the personal income tax deduction for building renovation (article 16-bis of Italy’s Tuir tax code) explicitly covers the installation of photovoltaic systems too, provided the system directly serves the home’s energy needs. Italy’s 2026 budget law (law no. 199/2025) extended the higher deduction rates into 2026, on this schedule:

Period the expense was incurred	Primary residence	Other cases	Spending cap
26/06/2012 - 31/12/2024	50%	50%	€96,000
2025 - 2026	50%	36%	€96,000
2027	36%	30%	€96,000
2028 - 2033	30%	30%	€48,000
from 2034	36%	36%	€48,000

Anyone installing a photovoltaic system or a storage battery must notify ENEA, Italy’s national energy research agency; for storage systems alone, this requirement has applied since January 1, 2019. A missing or late notification, though, doesn’t cause the loss of the tax deduction, according to a 2019 ruling by the Italian Revenue Agency.

The second tool concerns selling the electricity fed into the grid. The Ritiro Dedicato (RID) scheme lets producers sell electricity fed into the grid to the GSE, Italy’s energy services operator, at administered prices, and it’s open to a photovoltaic system of any size; the application must be filed within 60 days of the system coming online, the contract runs for a solar calendar year, and it renews automatically. For systems up to 100 kW, limited to the first 1.5 million kWh withdrawn each year, a guaranteed minimum price also applies, updated every year since 2014 based on the annual change in Istat consumer prices: if the market price is higher than the minimum, the GSE still pays the difference at year-end settlement, so producers always receive whichever value is more favorable. The exact guaranteed minimum price for 2026 hasn’t been verified against a primary source here; trade sources report a figure of around €0.0475/kWh, which should be treated with caution until confirmed by the official ARERA notice.

Anyone who installed a system in previous years may instead still have an active Scambio sul Posto (SSP) agreement, the net-metering mechanism that offset electricity fed in against electricity drawn from the grid: it has been closed to new applicants since 2025 (the last window was reserved for systems that came online by May 29, 2025, with applications filed with the GSE by September 26, 2025), though existing agreements continue until their natural expiration, never more than 15 years from the original signing. For anyone installing a system in 2026, then, the available option for grid-fed electricity is Ritiro Dedicato, not Scambio sul Posto.

How much solar power Italy has installed

Unlike a fossil-fuel power plant, a photovoltaic system burns nothing to produce electricity: the current comes directly from the photovoltaic effect in the cells, with no combustion and no direct emissions during operation — a difference that matters for the greenhouse effect, even though manufacturing the panels themselves has its own environmental footprint, discussed further below regarding end-of-life materials.

According to the IEA-PVPS report on Italy, cumulative national photovoltaic capacity stood at 37 GW at the end of 2024, with 6.7 GW of new capacity added during the year and 278,423 new systems, for a total of 1.88 million installations across the country; 55% of systems are located in northern Italy. In 2024, solar power generated 36 TWh of electricity, about 11.5% of national electricity consumption; the national plan cited in the report targets 80 GW of photovoltaic capacity by 2030.

The most recent data, reported by trade outlet PV Tech based on Terna/GSE figures, show that Italy installed 1.4 GW of new capacity in the first quarter of 2026: 560 MW from large ground-mounted systems (down 9% year on year), 313 MW residential (down 13%), and 566 MW commercial and industrial (up 24%). By the end of March 2026, cumulative national capacity had nearly reached 45 GW: it took about seven months to go from 40 to 45 GW. The figures above mostly describe concrete industrial growth, not yet even across every segment of the market.

Where and how to orient panels for the best output

Once the technology and system type are chosen, energy output depends largely on two practical variables: the panels’ orientation and tilt.

In Italy, the optimal orientation is generally south (180° azimuth), because at this latitude that’s the direction from which the most direct sunlight arrives over the course of the day. The optimal tilt, on the other hand, isn’t a single number that works everywhere: it varies with the latitude of the specific site, following a basic principle of solar geometry, and it also shifts slightly with small local obstacles (trees, nearby buildings, mountains on the horizon) that can cast shade on the panels at certain times of day.

To calculate the exact value for a specific address, the reference tool is PVGIS (Photovoltaic Geographical Information System), developed by the Joint Research Centre of the European Commission and available online for free, without registration, in several European languages. PVGIS estimates expected electricity output for any point on the globe except the poles, based on satellite irradiance data covering 2014-2024, and it includes two functions built exactly for this purpose: “Optimize slope,” which calculates the optimal tilt for a given orientation, and “Optimize slope and azimuth,” which calculates the optimal tilt and orientation together for the chosen location. The tool also lets users upload a horizon profile of local obstacles, useful for anyone with nearby trees or buildings that cast shade at certain hours of the day.

Practical example: before installing a system, or before evaluating a quote, someone can enter the exact address of their roof into PVGIS and run the “Optimize slope and azimuth” simulation: the tool returns the combination of orientation and tilt that maximizes estimated annual output for that precise location, instead of relying on a generic rule meant to apply to an entire country.

Straying far from the optimal orientation carries a measurable cost: according to simulations based on PVGIS data, orienting panels purely east or west, instead of south, brings an estimated production loss of 15-20% compared with the optimum. A southeast- or southwest-facing roof, more common than one facing perfectly south, loses far less: output stays relatively close to the optimum as long as the deviation from due south stays within a few dozen degrees.

Materials, lifespan, and end of life

A crystalline silicon module, the most common type in 2025, is built as a layered structure: an outer covering of tempered glass, an EVA (ethylene vinyl acetate) sealant in front of and behind the cells, cells connected to each other by metal ribbons made of copper, a rear backsheet made of polyvinyl fluoride (commercially known as Tedlar), and a perimeter frame made of aluminum — the same metal that, for its own properties, also shows up in window and door frames at home, valued for being lightweight and for being meltable and recyclable without losing its mechanical properties.

By weight, a crystalline silicon panel is made mostly of glass (65.8%, recyclable at a 97% rate) and aluminum (17.5%, recyclable at 100%), plus EVA (12.8%), silicon (2.9%, recyclable at 85%), and copper (1.0%, recyclable at 78%), according to a 2020 ENEA technical report: overall, about 90% of a panel’s weight is made of materials classified as non-hazardous, and modern technology can recover between 75 and 100% of the materials at end of life.

On lifespan, the harmonized assumptions Fraunhofer ISE uses to calculate energy payback time assume a system service life of 25 years, with an average production degradation rate of 0.70% per year and an average Performance Ratio, including degradation over time, of 73.6%. The energy payback time itself is surprisingly short: a system in Sicily using crystalline silicon modules recovers the energy spent building it in about a year; over the following 20 years of service, it can go on to produce up to 20 times the energy invested in building it.